Retroviruses have proven to be useful tools for investigating the processes of neoplastic transformation in mammalian cells. The majority of such studies have centered on the interactions of retroviruses with fibroblasts or hemapoietic cells. Few studies have been reported that deal with the effects of retroviral infection on cells of epithelial origin. The potential importance of such studies has been recently emphasized by the demonstration that dominant transforming genes isolated from human tumors are closely related to certain retroviral onc genes. We have recently isolated and characterized an epidermal keratinocyte cell line of murine origin designated Balb/MK, which is totally dependent on the presence of EGF for its continued proliferation. Upon exposure to extracellular levels of calcium greater than 1.0mM, these cells will terminally differentiate in a manner analogous to primary keratinocyte cultures. Transformation of these cells by Balb-, Harvey-or Kirsten-MSV results in the abrogation of the EGF requirement as well as a block in the pathway to calcium induced terminal differentiation. The research described in this proposal will investigate the interactions of other mammalian retroviruses on the growth and differentiation of Balb/MK cells. The effects of transformation by these different retroviruses on growth properties such as anchorage independent growth, growth factor requirements and transforming growth factor production will be compared. Specific stages of differentiation where these cells are blocked by various retroviruses will be identified by examining a variety of differentiated functions including production of cornified envelopes, desmosome formation, induction of transglutaminase activity and synthesis of different keratin species. Since both EGF and several retroviruses have been shown to stimulate protein kinase activity in cells, phosphorylation of tyrosine-containing proteins in these cells will also be determined.